The present invention relates to a pneumatic tire, more particularly to a tread pattern for a motorcycle tire capable of reducing the rolling resistance.
In the conventional motorcycle tires, there are widely employed tread patterns comprising a single central groove (a) extending continuously in the tire circumferential direction along the tire equator c and a plurality of oblique lateral grooves (b) arranged in a v-formation, as shown in FIG. 8 for example. In such conventional tread patterns, in order to secure a sufficient ground contacting area during straight running and thereby to provide the improved dry grip performance for the tire, the central groove (a) has a relatively narrow width of about 6 mm. Further, in order to improve the wet grip performance during straight running, the oblique lateral grooves (b) extend axially outwardly from the vicinity of the central groove (a), namely, the axially inner portions of the oblique lateral grooves (b) exist in the ground contacting region Yc during straight running.
In recent years, on the other hand, even in the motorcycle tires, it is strongly required to reduce the rolling resistance in order to decrease the fuel consumption of the motorcycles.
Therefore, the present inventor studied a tread pattern and found that the axially inner portions of the oblique lateral grooves (b), which exist in the ground contacting region Yc during straight running, are a large factor of the rolling resistance, and the rolling resistance can be reduced by eliminating the axially inner portions from the region Yc. But, if there is no groove in the region Yc, contrary to expectation, the rolling resistance is increased. The present inventor conducted experiments, making various tread patterns, and discovered that the rolling resistance of a motorcycle tore can be minimized when the ground contacting region Yc during straight running is provided with only circumferential grooves of a specific number and dimensions.